Crystal structure of Sr5Te4O12(OH)2, the first basic strontium oxotellurate(IV)

Weil, M.; Shirkhanlou, M.

doi:10.1107/S2056989016015577

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Volume 72| Part 11| November 2016| Pages 1532-1535

https://doi.org/10.1107/S2056989016015577

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Crystal structure of Sr₅Te₄O₁₂(OH)₂, the first basic strontium oxotellurate(IV)

Matthias Weil ^a ^* and Mahdi Shirkhanlou ^a

^aInstitute for Chemical Technologies and Analytics, Division of Structural Chemistry, Vienna University of Technology, Getreidemarkt 9/164-SC, A-1060 Vienna, Austria
^*Correspondence e-mail: matthias.weil@tuwien.ac.at

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 3 October 2016; accepted 4 October 2016; online 7 October 2016)

The asymmetric unit of the title basic strontium oxotellurate(IV), Sr₅Te₄O₁₂(OH)₂ {systematic name pentastrontium tetrakis[oxotellurate(IV)] dihydroxide}, comprises three Sr^II cations (one with site symmetry 2) and two Te^IV atoms, as well as seven O atoms. The coordination numbers of the alkaline earth cations to nearby O atoms range from seven (2 ×) to eight, and the Te^IV atoms are surrounded by three oxygen partners in the form of trigonal pyramids. The SrO_x polyhedra share corners and edges to build up a three-dimensional framework structure encapsulating channels propagating along [010]. The Te^IV atoms flank the framework O atoms and are situated at the outer array of the channels with the 5s² lone electron pairs protruding into the empty space of the channels (diameter ≃ 4 Å). Although the H atom of the OH group could not be located, bond-valence-sum calculations and typical O⋯O distances (range 2.81–3.06 Å) clearly indicate hydrogen bonding of medium to weak strengths.

Keywords: crystal structure; strontium tellurite; channel structure; stereoactive electron lone pair.

CCDC reference: 1508062

1. Chemical context

The peculiar feature of the crystal chemistry of oxotellurates(IV) (Christy et al., 2016 ) is the presence of the 5s² lone electron pair, denoted E. In the majority of cases, the lone electron pair E is stereochemically active, making oxotellurates(IV) interesting for crystal engineering, e.g. in terms of the synthesis of compounds with non-centrosymmetric structures or structures with polar directions. Next to the influence of the (metal) cation on the physico-chemical characteristics of oxotellurates(IV), physical and underlying structural properties of such compounds can also be varied by incorporation of other oxoanions into the oxotellurate(IV) framework, e.g. by p-block oxoanions such as nitrate (Stöger & Weil, 2013 ) or selenate (Weil & Shirkanlou, 2015 ), or by d-block oxoanions such as vanadate (Weil, 2015 ).

In this context we attempted the hydrothermal synthesis of new oxotellurate phases in the system Sr–Te–Se–O–(H). In comparison with typical solid-state reactions using open crucibles under atmospheric conditions, this method is more feasible because Te^IV then tends not to be oxidized or to be evaporated during the reaction process. However, a clear disadvantage of the hydrothermal method is the high(er) number of adjustable parameters (pressure, concentration, temperature, time, filling degree, solvent etc), which often makes the products of these experiments difficult to predict or even to reproduce, accompanied by formation of several solid phases in one batch. This was also the case for the present study. Instead of a strontium oxoselenatotellurate, several oxotellurate phases were obtained without incorporation of selenium. Amongst these phases, the title compound, Sr₅Te₄O₁₂(OH)₂, a hitherto unknown strontium oxotellurate, was isolated and structurally determined by single crystal X-ray diffraction.

2. Structural commentary

The asymmetric unit of Sr₅Te₄O₁₂(OH)₂ comprises three Sr, two Te and seven O atoms (H atoms were not included in the final model, see Section 5 and discussion below). Except one Sr atom (Sr2) that is located on a twofold rotation axis, all atoms are in general positions.

The coordination numbers of the Sr atoms are 7 (for Sr1 and Sr3) and 8 (for Sr2) if Sr—O distances < 3.0 Å are considered as relevant for the first coordination sphere. The corresponding polyhedra are considerably distorted, with Sr—O bond lengths ranging from 2.393 (11) to 2.960 (11) Å (Table 1) and might be described as monocapped octahedra for Sr1 and Sr3, and as a bicapped trigonal prism for Sr2. The SrO₈ and the two SrO₇ polyhedra share corners and edges, thereby constructing a three-dimensional framework structure encapsulating channels that propagate along [010]. Each of the two Te atoms connect to the outer oxygen atoms of the framework in a very similar trigonal-prismatic configuration (Table 1), with the 5s² lone electron pair E being stereochemically active, i.e. pointing towards the empty space of the channels (Fig. 1). The channel diameter (without contribution of the lone pairs) is ≃ 4 Å. Te—O bond lengths [1.865 (11)–1.890 (12) Å for Te1 and 1.858 (11)–1.886 (11) Å for Te2] and O—Te—O angles [98.0 (5)–100.3 (5)° for Te1 and 98.8 (5)—101.1 (5)° for Te2] are typical for oxotellurate(IV) anions with three oxygen partners (Christy et al., 2016).

Table 1
Selected geometric parameters (Å, °)

Sr1—O7	2.430 (12)	Sr3—O2	2.507 (11)
Sr1—O5ⁱ	2.476 (12)	Sr3—O4^v	2.517 (11)
Sr1—O1ⁱⁱ	2.593 (12)	Sr3—O6ⁱ	2.536 (11)
Sr1—O3	2.596 (11)	Sr3—O6^vi	2.590 (12)
Sr1—O2ⁱⁱⁱ	2.616 (12)	Sr3—O4^vii	2.644 (11)
Sr1—O7ⁱⁱⁱ	2.700 (11)	Sr3—O1^viii	2.666 (11)
Sr1—O2	2.852 (12)	Te1—O6	1.865 (11)
Sr2—O3	2.510 (11)	Te1—O2	1.871 (11)
Sr2—O1^iv	2.624 (12)	Te1—O5	1.890 (12)
Sr2—O5	2.633 (12)	Te2—O4	1.858 (11)
Sr2—O7	2.960 (11)	Te2—O3	1.882 (11)
Sr3—O7ⁱⁱⁱ	2.393 (11)	Te2—O1	1.886 (11)

O6—Te1—O2	99.4 (4)	O4—Te2—O3	101.1 (5)
O6—Te1—O5	100.3 (5)	O4—Te2—O1	100.3 (5)
O2—Te1—O5	98.0 (5)	O3—Te2—O1	98.8 (5)
Symmetry codes: (i) x, y-1, z; (ii) -x, y, -z+1; (iii) $[-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z+1]$ ; (iv) -x, y+1, -z+1; (v) $[x+{\script{1\over 2}}, y-{\script{1\over 2}}, z]$ ; (vi) $[-x+{\script{1\over 2}}, y-{\script{1\over 2}}, -z]$ ; (vii) -x, y, -z; (viii) $[x+{\script{1\over 2}}, y+{\script{1\over 2}}, z]$ .

Figure 1
Projection of the crystal structure of Sr₅Te₄O₁₂(OH)₂ along [010], with displacement ellipsoids drawn at the 74% probability level. The trigonal–pyramidal TeO₃ groups are given in red; the O atom representing the OH group is given in yellow, all other O atoms are colourless.

Bond-valence calculations (Brown, 2002 ) clearly reveal the presence of an OH group for atom O7 (Table 2), also required by charge neutrality. Atom O7 is bonded to four Sr atoms (Table 1, Fig. 1) and has also four possible oxygen acceptor atoms for hydrogen bonding of medium to weak strength (Table 3). The situation of four possible acceptor atoms is displayed in Fig. 2 and makes it appear likely that the corresponding H atom of the OH group is positionally disordered and thus could not be located during the present study.

Table 2
Results of the bond-valance-sum (BVS) analysis

Atom	BVS	Δ to expected value
Sr1	2.07	0.07
Sr2	1.91	0.09
Sr3	2.23	0.23
Te1	3.94	0.06
Te2	3.93	0.07
O1	2.04	0.04
O2	2.08	0.08
O3	1.91	0.09
O4	1.96	0.04
O5	1.89	0.11
O6	1.95	0.05
O7	1.21	0.79
BVS parameters of Brown & Altermatt (1985 ) were used for all bonds.

Table 3
Hydrogen-bond geometry (Å)

D—H⋯A	D⋯A
O7⋯O5	2.808 (12)
O7⋯O2	2.893 (12)
O7⋯O2^ix	2.991 (11)
O7⋯O1^iv	3.063 (11)
Symmetry codes: (iv) -x, y+1, -z+1; (ix) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, -z+1]$ .

Figure 2
The vicinity of the OH group emphasizing the different possibilities for O⋯O hydrogen bonding (green lines). Sr—(OH) bonds have been omitted for clarity. Symmetry operators refer to those of Table 3

; displacement ellipsoids are the same as in Fig. 1

In the sense of a crystal-chemically more detailed formula, the title compound may alternatively be formulated as 4SrTeO₃·Sr(OH)₂ and represents the first basic strontium oxotellurate(IV), viz. with the presence of an OH functionality. In comparison with the other strontium oxotellurates(IV) compiled in Section 3, all Sr—O and Te—O lengths are in similar ranges.

3. Database survey

In the Inorganic Crystal Structure Database (ICSD, 2016 ) structural data for the following hydrous or anhydrous strontium oxotellurate(IV) phases have been deposited: SrTe₅O₁₁ (Burckhardt & Trömel, 1983 ), Sr₃Te₄O₁₁ (Dytyatyev & Dolgikh, 1999 ), various polymorphs of SrTeO₃ (Dityatiev et al., 2006 ; Zavodnik et al., 2007a ,b ,c , 2008 ; Stöger et al., 2011 ), SrTe₃O₈ (Barrier et al., 2006 ; Weil & Stöger, 2007 ) and SrTeO₃(H₂O) (Stöger et al., 2011). Additionally, in the International Centre for Diffraction Data PDF-4 database (ICDD, 2015 $[ICDD (2015). PDF-4+ 2015 Database, edited by S. Kabekkodu. International Centre for Diffraction Data, Newtown Square, PA, USA.]$ ) diffraction data for the following phases are compiled: Sr₂Te₃O₈ (Elerman & Koçak, 1986 ), SrTe₂O₅ (Redman et al., 1970 ; Gorbenko et al., 1983 ) and a high-temperature phase of the latter (Külcü et al., 1984 ).

4. Synthesis and crystallization

For the hydrothermal experiment, a Teflon container was filled with 0.0733 g of strontium oxide, 0.1529 g of tellurium dioxide and 0.032 ml of selenic acid (conc.; 96 wt%), corresponding to the stoichiometric ratio 3:2:1. To this mixture 10 ml water were added to about three-fourth of the container volume. The container was then sealed with a Teflon lid and loaded into a stainless steel autoclave and then heated at autogenous pressure in an oven at 403 K for one week. After the reaction time, the autoclave was allowed to cool down to room temperature over six h. The formed solid product was filtered off and washed with water and ethanol. Inspection under a polarizing microscope revealed a phase mixture with different crystal forms clearly discernible. According to X-ray powder diffraction of the bulk material, the following phases could be identified: α-TeO₂ (Lindqvist, 1968 ), SrTe₂O₅ (Redman et al., 1970), SrTe₃O₈ (Barrier et al., 2006; Weil & Stöger, 2007) and SrTe₅O₁₁ (Burckhardt & Trömel, 1983). Solid reaction products containing Se-phases were not detected. Platy Sr₅Te₄O₁₂(OH)₂ crystals were present in only minor amounts, and were manually separated for structure determination from the other solid products.

5. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 4. Some of the O atoms showed physically unreasonable behaviour when refined with anisotropic displacement parameters. Hence, for the final model all O atoms were refined with individual isotropic displacement parameters. The H atom of the OH group (or positionally disordered parts) could not be located and thus was not included in the model. Twinning by inversion was also taken into account, with a contribution of the minor twin component of about 6%. The maximum and minimum remaining electron densities are found 2.34 and 0.96 Å, respectively, from Sr3.

Table 4
Experimental details

Crystal data
Chemical formula	Sr₅Te₄O₁₂(OH)₂
M_r	1174.52
Crystal system, space group	Monoclinic, C2
Temperature (K)	295
a, b, c (Å)	16.0785 (10), 5.7927 (5), 8.9262 (7)
β (°)	107.542 (4)
V (Å³)	792.71 (11)
Z	2
Radiation type	Mo Kα
μ (mm⁻¹)	23.99
Crystal size (mm)	0.18 × 0.06 × 0.01

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Bruker, 2012 )
T_min, T_max	0.099, 0.795
No. of measured, independent and observed [I > 2σ(I)] reflections	12913, 1914, 1319
R_int	0.088
(sin θ/λ)_max (Å⁻¹)	0.660

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.042, 0.085, 1.02
No. of reflections	1914
No. of parameters	71
No. of restraints	1
H-atom treatment	H-atom parameters not defined
Δρ_max, Δρ_min (e Å⁻³)	2.31, −1.78
Absolute structure	Refined as an inversion twin
Absolute structure parameter	0.058 (18)
Computer programs: APEX2 and SAINT (Bruker, 2012), SHELXS97 (Sheldrick, 2008 ), SHELXL2014 (Sheldrick, 2015 ), ATOMS (Dowty, 2006 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 1508062

Crystal structure: contains datablocks I, global. DOI: https://doi.org/10.1107/S2056989016015577/hb7619sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989016015577/hb7619Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ATOMS (Dowty, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).

Pentastrontium tetrakis[oxotellurate(IV)] dihydroxide top

Crystal data top

Sr₅Te₄O₁₂(OH)₂	F(000) = 1024
M_r = 1174.52	D_x = 4.921 Mg m⁻³
Monoclinic, C2	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: C 2y	Cell parameters from 2028 reflections
a = 16.0785 (10) Å	θ = 4.2–33.0°
b = 5.7927 (5) Å	µ = 23.99 mm⁻¹
c = 8.9262 (7) Å	T = 295 K
β = 107.542 (4)°	Plate, colourless
V = 792.71 (11) Å³	0.18 × 0.06 × 0.01 mm
Z = 2

Data collection top

Bruker APEXII CCD diffractometer	1319 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	R_int = 0.088
ω and φ scans	θ_max = 28.0°, θ_min = 2.4°
Absorption correction: multi-scan (SADABS; Bruker, 2012)	h = −20→21
T_min = 0.099, T_max = 0.795	k = −7→7
12913 measured reflections	l = −11→11
1914 independent reflections

Refinement top

Refinement on F²	H-atom parameters not defined
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0236P)² + 0.7139P] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.042	(Δ/σ)_max < 0.001
wR(F²) = 0.085	Δρ_max = 2.31 e Å⁻³
S = 1.02	Δρ_min = −1.78 e Å⁻³
1914 reflections	Absolute structure: Refined as an inversion twin
71 parameters	Absolute structure parameter: 0.058 (18)
1 restraint

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refined as a 2-component inversion twin

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Sr1	0.16911 (10)	0.0360 (4)	0.4988 (2)	0.0097 (5)
Sr2	0.0000	0.5471 (4)	0.5000	0.0094 (8)
Sr3	0.27399 (11)	0.0613 (2)	0.1447 (2)	0.0071 (5)
Te1	0.10820 (7)	0.52512 (19)	0.16455 (15)	0.0081 (3)
Te2	−0.05011 (7)	0.0246 (2)	0.17800 (14)	0.0091 (3)
O1	−0.0998 (7)	−0.1557 (19)	0.3050 (14)	0.015 (3)*
O2	0.2040 (8)	0.3491 (18)	0.2785 (14)	0.017 (3)*
O3	0.0218 (7)	0.2152 (19)	0.3350 (14)	0.013 (3)*
O4	−0.1423 (7)	0.2229 (19)	0.0869 (14)	0.018 (3)*
O5	0.0964 (7)	0.7088 (19)	0.3320 (14)	0.017 (3)*
O6	0.1651 (7)	0.7327 (19)	0.0690 (14)	0.014 (3)*
O7	0.1881 (7)	0.4343 (18)	0.5881 (13)	0.017 (3)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Sr1	0.0090 (8)	0.0107 (11)	0.0086 (10)	−0.0015 (8)	0.0013 (7)	−0.0017 (9)
Sr2	0.0108 (13)	0.006 (2)	0.0134 (14)	0.000	0.0063 (10)	0.000
Sr3	0.0055 (8)	0.0035 (13)	0.0127 (10)	−0.0001 (7)	0.0036 (6)	−0.0012 (9)
Te1	0.0066 (6)	0.0084 (8)	0.0087 (6)	0.0003 (6)	0.0014 (4)	0.0000 (6)
Te2	0.0092 (6)	0.0062 (7)	0.0126 (7)	−0.0013 (7)	0.0041 (4)	−0.0024 (8)

Geometric parameters (Å, º) top

Sr1—O7	2.430 (12)	Sr3—O2	2.507 (11)
Sr1—O5ⁱ	2.476 (12)	Sr3—O4^vi	2.517 (11)
Sr1—O1ⁱⁱ	2.593 (12)	Sr3—O6ⁱ	2.536 (11)
Sr1—O3	2.596 (11)	Sr3—O6^vii	2.590 (12)
Sr1—O2ⁱⁱⁱ	2.616 (12)	Sr3—O4^viii	2.644 (11)
Sr1—O7ⁱⁱⁱ	2.700 (11)	Sr3—O1^ix	2.666 (11)
Sr1—O2	2.852 (12)	Te1—O6	1.865 (11)
Sr2—O3	2.510 (11)	Te1—O2	1.871 (11)
Sr2—O3ⁱⁱ	2.510 (11)	Te1—O5	1.890 (12)
Sr2—O1^iv	2.624 (12)	Te2—O4	1.858 (11)
Sr2—O1^v	2.624 (11)	Te2—O3	1.882 (11)
Sr2—O5	2.633 (12)	Te2—O1	1.886 (11)
Sr2—O5ⁱⁱ	2.633 (12)	O7—O1^iv	3.063 (11)
Sr2—O7ⁱⁱ	2.960 (11)	O7—O2	2.893 (12)
Sr2—O7	2.960 (11)	O7—O2^x	2.991 (11)
Sr3—O7ⁱⁱⁱ	2.393 (11)	O7—O5	2.808 (12)

O7—Sr1—O5ⁱ	156.1 (4)	O2—Sr3—O6ⁱ	104.7 (4)
O7—Sr1—O1ⁱⁱ	102.8 (4)	O4^vi—Sr3—O6ⁱ	74.3 (3)
O5ⁱ—Sr1—O1ⁱⁱ	81.8 (4)	O7ⁱⁱⁱ—Sr3—O6^vii	144.4 (4)
O7—Sr1—O3	79.0 (4)	O2—Sr3—O6^vii	114.8 (4)
O5ⁱ—Sr1—O3	77.4 (4)	O4^vi—Sr3—O6^vii	78.7 (4)
O1ⁱⁱ—Sr1—O3	92.7 (4)	O6ⁱ—Sr3—O6^vii	118.4 (3)
O7—Sr1—O2ⁱⁱⁱ	98.7 (4)	O7ⁱⁱⁱ—Sr3—O4^viii	142.3 (4)
O5ⁱ—Sr1—O2ⁱⁱⁱ	105.0 (4)	O2—Sr3—O4^viii	76.6 (4)
O1ⁱⁱ—Sr1—O2ⁱⁱⁱ	72.8 (4)	O4^vi—Sr3—O4^viii	117.8 (3)
O3—Sr1—O2ⁱⁱⁱ	164.5 (4)	O6ⁱ—Sr3—O4^viii	74.4 (3)
O7—Sr1—O7ⁱⁱⁱ	105.5 (3)	O6^vii—Sr3—O4^viii	71.3 (3)
O5ⁱ—Sr1—O7ⁱⁱⁱ	87.0 (4)	O7ⁱⁱⁱ—Sr3—O1^ix	74.3 (4)
O1ⁱⁱ—Sr1—O7ⁱⁱⁱ	132.6 (4)	O2—Sr3—O1^ix	73.4 (4)
O3—Sr1—O7ⁱⁱⁱ	129.5 (4)	O4^vi—Sr3—O1^ix	102.8 (3)
O2ⁱⁱⁱ—Sr1—O7ⁱⁱⁱ	65.9 (4)	O6ⁱ—Sr3—O1^ix	163.2 (4)
O7—Sr1—O2	65.9 (4)	O6^vii—Sr3—O1^ix	76.3 (3)
O5ⁱ—Sr1—O2	103.2 (4)	O4^viii—Sr3—O1^ix	120.2 (3)
O1ⁱⁱ—Sr1—O2	162.2 (4)	O6—Te1—O2	99.4 (4)
O3—Sr1—O2	72.1 (3)	O6—Te1—O5	100.3 (5)
O2ⁱⁱⁱ—Sr1—O2	121.1 (2)	O2—Te1—O5	98.0 (5)
O7ⁱⁱⁱ—Sr1—O2	65.2 (3)	O4—Te2—O3	101.1 (5)
O3—Sr2—O3ⁱⁱ	80.0 (5)	O4—Te2—O1	100.3 (5)
O3—Sr2—O1^iv	136.6 (4)	O3—Te2—O1	98.8 (5)
O3ⁱⁱ—Sr2—O1^iv	106.2 (3)	Te2—O1—Sr1ⁱⁱ	121.0 (5)
O3—Sr2—O1^v	106.2 (3)	Te2—O1—Sr2ⁱ	118.5 (5)
O3ⁱⁱ—Sr2—O1^v	136.6 (4)	Sr1ⁱⁱ—O1—Sr2ⁱ	97.7 (4)
O1^iv—Sr2—O1^v	98.0 (5)	Te2—O1—Sr3^xi	114.2 (5)
O3—Sr2—O5	74.2 (3)	Sr1ⁱⁱ—O1—Sr3^xi	102.3 (4)
O3ⁱⁱ—Sr2—O5	144.8 (4)	Sr2ⁱ—O1—Sr3^xi	99.6 (4)
O1^iv—Sr2—O5	78.3 (4)	Te1—O2—Sr3	121.2 (6)
O1^v—Sr2—O5	74.7 (3)	Te1—O2—Sr1^x	120.9 (5)
O3—Sr2—O5ⁱⁱ	144.8 (4)	Sr3—O2—Sr1^x	106.2 (4)
O3ⁱⁱ—Sr2—O5ⁱⁱ	74.2 (3)	Te1—O2—Sr1	114.9 (5)
O1^iv—Sr2—O5ⁱⁱ	74.7 (3)	Sr3—O2—Sr1	96.6 (3)
O1^v—Sr2—O5ⁱⁱ	78.3 (4)	Sr1^x—O2—Sr1	90.5 (4)
O5—Sr2—O5ⁱⁱ	138.3 (5)	Te2—O3—Sr2	136.3 (5)
O3—Sr2—O7ⁱⁱ	89.3 (3)	Te2—O3—Sr1	115.9 (5)
O3ⁱⁱ—Sr2—O7ⁱⁱ	71.0 (3)	Sr2—O3—Sr1	103.9 (4)
O1^iv—Sr2—O7ⁱⁱ	133.8 (3)	Te2—O4—Sr3^xii	142.8 (6)
O1^v—Sr2—O7ⁱⁱ	66.2 (3)	Te2—O4—Sr3^viii	117.9 (5)
O5—Sr2—O7ⁱⁱ	131.1 (3)	Sr3^xii—O4—Sr3^viii	94.8 (4)
O5ⁱⁱ—Sr2—O7ⁱⁱ	60.0 (3)	Te1—O5—Sr1^v	139.9 (6)
O3—Sr2—O7	71.0 (3)	Te1—O5—Sr2	117.8 (5)
O3ⁱⁱ—Sr2—O7	89.3 (3)	Sr1^v—O5—Sr2	100.5 (4)
O1^iv—Sr2—O7	66.2 (3)	Te1—O6—Sr3^v	139.1 (6)
O1^v—Sr2—O7	133.8 (3)	Te1—O6—Sr3^xiii	115.9 (5)
O5—Sr2—O7	60.0 (3)	Sr3^v—O6—Sr3^xiii	95.7 (4)
O5ⁱⁱ—Sr2—O7	131.1 (3)	Sr3^x—O7—Sr1	126.0 (5)
O7ⁱⁱ—Sr2—O7	154.5 (4)	Sr3^x—O7—Sr1^x	103.7 (4)
O7ⁱⁱⁱ—Sr3—O2	75.2 (4)	Sr1—O7—Sr1^x	98.5 (4)
O7ⁱⁱⁱ—Sr3—O4^vi	88.5 (4)	Sr3^x—O7—Sr2	97.4 (4)
O2—Sr3—O4^vi	163.7 (4)	Sr1—O7—Sr2	96.0 (4)
O7ⁱⁱⁱ—Sr3—O6ⁱ	89.0 (4)	Sr1^x—O7—Sr2	139.9 (4)

Symmetry codes: (i) x, y−1, z; (ii) −x, y, −z+1; (iii) −x+1/2, y−1/2, −z+1; (iv) −x, y+1, −z+1; (v) x, y+1, z; (vi) x+1/2, y−1/2, z; (vii) −x+1/2, y−1/2, −z; (viii) −x, y, −z; (ix) x+1/2, y+1/2, z; (x) −x+1/2, y+1/2, −z+1; (xi) x−1/2, y−1/2, z; (xii) x−1/2, y+1/2, z; (xiii) −x+1/2, y+1/2, −z.

Hydrogen-bond geometry (Å) top

D—H···A	D···A
O7···O5	2.808 (12)
O7···O2	2.893 (12)
O7···O2^x	2.991 (11)
O7···O1^iv	3.063 (11)

Symmetry codes: (iv) −x, y+1, −z+1; (x) −x+1/2, y+1/2, −z+1.

Results of the bond-valance-sum (BVS) analysis top

Atom	BVS	Δ to expected value
Sr1	2.07	0.07
Sr2	1.91	0.09
Sr3	2.23	0.23
Te1	3.94	0.06
Te2	3.93	0.07
O1	2.04	0.04
O2	2.08	0.08
O3	1.91	0.09
O4	1.96	0.04
O5	1.89	0.11
O6	1.95	0.05
O7	1.21	0.79

BVS parameters of Brown & Altermatt (1985) were used for all bonds.

Acknowledgements

The X-ray centre of the Vienna University of Technology is acknowledged for providing access to the single-crystal diffractometer.

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